After reading up on the for and against views of the BPV spring upgrade, I decided to do a before and after... or rather... an after and before test on my car.

I currently have a Hahn IC installed on my car. When I got it installed, I installed the BPV spring the very next day, so I didn't get that much time with just the IC on it and therefore didn't know what performance characteristics could be attributed to the new IC or spring (should have waited a while in between mods looking back on it so I could tell).

I've driven roughly 2,000 miles with the spring installed, from 8,500 to 10,500 miles on the odometer.

My plan was to drive the car, let it cool, replace the BPV spring with the stock one, and then drive it again, looking at the same parameters and feel.

My conclusion is as follows:
- The turbo response is far better with the stock spring, believe it or not.
- Fuel economy is inconclusive. I couldn't tell much difference, if any. There was wind while I was going down the highway, so I did a roundabout average of going both directions for several miles.
- The BPV spring has a leg up on sound agressiveness. You can only get this sound during high load/high rev shifting with the stocker. It's more of a muffled chirp versus the stocker's muffled whoosh.
- Peak boost was identical, while overall the stock boost was between 0-2 psi lower in some of the RPM range during WOT acceleration.

Due to the huge difference in turbo response with the stocker, I'm led to believe that the possibility of flutter may be present. There have been several times with the upgrade that it takes a while in between shifts to get my boost back or it falls on it's face when I'm suddenly getting on it at low speed. I previously thought this was because of the increased volume of the IC that the non-tuned setup I have had to fill. It is no longer present at all. This tells me that the compressor is slowing more between shifts, which means the BPV isn't doing it's job very well and the backflow boost pressure may be making it to the compressor and slowing it (flutter).

The turbo itself seems to sound a bit different during driving on the highway too... just a neutral discovery. In addition, another neutral, it just "feels" different from a stop during stop-and-go, although I'm not sure exactly what is that I'm feeling. I also never had any "rubber band-ing" or "bucking" even once while on the upgrade.

Final Verdict: After what I've witnessed, I plan on going with the stock spring now. The turbo response difference made such an impact that it won me over. I prefer the "whoosh" sound too, so if I want to bring that out, an intake would probably be the ticket anyway. An intake will bring out either sound better though.


Hope this helps, or at least gives people answers to some of their questions and something to think about.

Some comparison pictures from tonight. Silver one is upgraded spring. Darker is stock spring:

 

Nice work man. Compelling evidence. I'm sure there will be people that won't agree for one reason or another, but for me I'm going to stick with the stocker.

 

Very interesting-I just installed one a few days ago and noticed the crisper "chirping" sound. I got on it a couple of times and didn't notice any difference in performance however I haven't "tested" it much and I was trying to notice a gain(rather than a loss). Also, recently I was checking some early threads in the LNF section and I seem to recall someone mentioning the spring and possible "turbo flutter". I wasn't expecting too much @ this point from a $10 spring but I don't want to take a step back or jeapordize anything.

 

Does anyone know if there are any benefits of the upgraded spring if you have a tune?

 

I have the spring on my car....

Got it after my tune which is VERY damn aggressive!

I have quicker spool up over stock, quicker bypass (opening and closing)

Gas milage has improved (prolly the tune though)...

I am glad I got the mod myself, I have seen my does hold boost more consistant, no spikes.... from 0-22.25 psi and holds!

Just my opinion!

 

i just ordered it but I have an intake. hoping maybe that will increase spool time. we will see

 

Intake does increase... but charge pipes seem to help the most with spool time!

 

Thanks for taking the time to compare. I'm pretty much convinced not to put this thing in. I prefer the whoosh sound anyway. My car is not a canary.

 

also learn down feature has to be taken into account

 

Not tuned either are you......

Thats like adding an intake/exhaust to the stock car...Its pointless as the computer will correct and de-tune itself for you. But when your pushing 22psi "re-do" your test.

 

Since a majority of people here aren't tuned right now, I figured it would be pertinent. I could help with real-life findings, such as turbo response and gas mileage in close-to-stock configuration, which one wouldn't be touched by learn-down and the other is a byproduct of learn-down (and wasn't noticably different either). Also, wouldn't having a tune create yet another changing variable? Not too many people have the exact same tune. Even Trifecta/canned tunes have customizeable options on them which could cause a difference in findings.

On that note though, tuned setups may have different findings then what I found.

It would be interesting indeed if somebody else with a tune could do a similar test with theirs.

I did as best as I could to take this variable out, by starting it, letting it idle for a while, starting it again and driving it for a while, shutting it down again, and then conducting the test over two more key cycles. I imagine the learn-down should have done its thing by the time I conducted the actual "before" test again.

 

I would think most that are doing this upgrade are doing it because they are tuned. Why do anything to this car if your not tuned?


Answer is from Bill Hahn in talking about his upgrade for the GXP/RL. I'm sure many of us plan on upgrading to something that has more potential down the road. Until then, there is a difference in tuned vs un-tuned in the amount of flow we are asking the BPV/BOV to work with. I'm waiting to see what Hahn comes out with before I go with anything else, but until then I run the 10.00 spring upgrade

 

thanks for the great info

 

Well, let's take the theory behind the spring, for instance. The spring has a higher tension, meaning that it takes more engine suction to open the valve. If more engine suction is needed to open the valve, then the throttle plate must close more to cause this suction on the other side of the throttle plate/in the manifold and therefore pull the valve open.

This extra time/delay is what makes the sound louder, as it lets the pressure rise higher inside the boost piping before opening the valve, causing a louder sound (the reason you can't get the same sound with the stocker unless you're running it hard).

The upside is that you get a more noticeable sound... the downside is that the pressure rises higher inside the boost tubing and onto the face of the compressor until it's relieved, slowing/fluttering the compressor (which explains the longer time it takes to spool back up between shifts and the flutter people have been reporting).

The physics of the system stays constant whether tuned or not.

I believe Mr. Hahn wasn't referring to a spring inside the BPV, but is referring to an altogether revised method that allows for more flow when activated that insures that the pressure within the boost piping doesn't back up to the face of the turbo compressor. When pressure is higher, that means more air mass is inside the boost piping and therefore a way to release more air in one bypass needs to be installed. It says it right there in his quote that it's the amount of flow out the valve that needs to be increased when tuned.

Now think about this: That valve can only bypass so much air in a certain amount of time. If you put a spring on it that doesn't trip until later, then where does the air go that's waiting to go somewhere inside the boost piping? The throttle plate is closed/closing, so the only way to go is towards the turbo. In a tuned configuration, when boost is turned up even more, then you have even more air and pressure waiting to go out the valve, aggrivating this issue. The answer then is to have a weaker spring that would trip sooner rather then later (unless you're going with an alternative BPV setup) so that increased air mass can bypass.

 

This is the issue w/ push type BPV/BOV....Do you want surge @ lower RPS or once you let off the gas with full boost pressure then? IF you want it at higher RPMS and lower RPMS stay w/ the stock spring. If you want to make sure the valve as every opportunity to close @ higher boost lvls, get the upgraded spring. The spring is for closing the valve, not opening the valve. Engine Vacum will open the valve, and your right, at really low RPMS I'm sure a stock car see's issues, but again that is the case with stock spring as well, its a nature of design for our cars. Like I said, its not a perfect solution, and since I have the hahn charge piping already, I'm waiting to see what they come out with on their setup, I already have the Dejon pipe w/ the recirc valve welded in place just in case.

 

So what is the finally decision Is this thing good or bad? Im considering taking mine out...

 

Going on 2000 miles on mine... without any issues to report.

 

In actuality, the Dejon BPV spring, because it has a greater spring rate, opens too late after you let off sometimes causing that flutter noise (compressor surge). It is purely a sound mod only. The stock spring as a 8 lb/inch spring rate and Dejons is 13 lbs/inch so it takes only 8 lbs of vac when you let off to open the stock BPV an inch but it takes 13 lbs of vac to open the BPV the same amount with the Dejon spring. As for those who cry boost leaks. BS. The pressure plus the spring tension seals the BPV diaphram when under pressure. When you let off the vac from the intake (black hose that connects to the tan cover supplies it) opens the BPV and the excess air is vented. There you go.

 

8 lbs of vacuum is -16 inHg. 13 lbs of vacuum is 26 in HG. 13 lbs is way to stiff. The reason it's more responsive is because until you hit -16 inHg, the BPV remains open allowing air to bypass the turbo making it easier for the turbo to spool up because the motor doesn't have to initially suck air through the compressor housing.

 

Final Verdict: After what I've witnessed, I plan on going with the stock spring now. The turbo response difference made such an impact that it won me over. I prefer the "whoosh" sound too, so if I want to bring that out, an intake would probably be the ticket anyway. An intake will bring out either sound better though.


Yep, I just went back to the stocker today. Actually, it's weird about the spool up time. Totally didn't expect that but you're right. I noticed immediately that the turbo spool up response time was FAR better with the stocker.
I know what you mean about the stop and go too. Hard to describe it though. I guess the closest thing you could say is the difference between turbo lag and an NA car. Even though turbo lag isn't actually coming into play here. I don't know any other way to describe the feeling. Just a more instant, urgent, and yet smoother take off from a stop - just daily driving it too.
Just a matter of opinion I know, but I also prefer the "whoosh" sound too. Thanks for the write up!

 

I think you guys are making stuff up, or having things in your head. Now with these responces of slow spool? Are you guys stock or tuned...

I know all of us tuned guys are seeing the opposite!

 

Tuned...

Not making stuff up man. I had the Dejon spring in for maybe 6k miles. Took advantage of boost quite a bit. Went back to stock today.
It's not hard to do obviously, just go back to the stocker for a bit and see for yourself.

 

Taking this out as soon as I recover from surgery.

 

LOL reviving a dead thread FTW

Good move man. Im more partial to the Forge Motorsports full BPV upgrade rather than just a spring.